Method for transmitting data

ABSTRACT

A method is described for transmitting data between participants of a serial, ring-shaped communications arrangement in which the participants are serially connected to one another, wherein a data packet is passed from a participant provided as a master to further participants provided as slaves, wherein the data packet is passed from slave to slave, and wherein address information of the data packet is altered by each slave.

RELATED APPLICATION INFORMATION

The present application is a divisional application of U.S. patentapplication Ser. No. 13/245,311, filed on Sep. 26, 2011, which claimspriority to and the benefit of German Patent Application No. 10 2010 041427.1, which was filed in Germany on Sep. 27, 2010, the contents of eachof which are hereby incorporated in the accompanying application byreference in their entireties.

FIELD OF THE INVENTION

The present invention relates to a method for transmitting data betweenparticipants of a communications arrangement, and to a communicationsarrangement.

BACKGROUND INFORMATION

In many networks, more often serial interfaces are used instead ofparallel interfaces. The reasons for this are the reduction in costs forthe layout and connection technology, for example the number of pins,simplification of the system design and scalability of the bandwidth oftransmission data by parallel use of a plurality of serial interfaces.

This trend is becoming apparent particularly in the field of consumerelectronics with a large number of serial interface standards. Thosestandards are used mostly for communication with peripheral devices, forexample hard drives or displays. Apart from the small number of pins,however, those interfaces make use of complex protocols, which requirehigh expenditure in terms of implementation. For data transmissionbetween logic components (ICs), for example on the mainboard of a PC orwithin a handheld device, present-day interfaces bundle a plurality ofserial data streams, for example PCI-Express or Quickpath, and therebyenable the system designer to scale the bandwidth.

In the automotive engineering sector, serial interfaces (SPI, serialperipheral interfaces) are used for data transmission between logiccomponents, which may be in the form of integrated circuits (IC), incontrol units. That standard describes bidirectional, synchronous andserial data transmission between a component provided as a master andvarious components provided as slaves. An interface includes in thiscase at least three lines between the master and a slave, these normallybeing two data lines and a clock line. In the case of a plurality ofslaves, each of those components requires an additional select line fromthe master. The SPI interface enables a daisy-chain or bus topology tobe implemented.

In some cases, the SPI interface is not suitable for the transmission oftime-critical actuation signals in order to meet the real-timerequirements of present-day safety applications, for example ESP.Frequently, only an exchange of diagnostic and status information takesplace with an SPI interface. Time-critical actuation signals arenormally transmitted to the actuation components of the actuators and/orfrom the evaluation circuits of the sensors at great expense using timerunits and/or proprietary interfaces.

When used in the form of a bus topology, at higher data rates the SPIinterface gives rise to increasingly poorer signal integrities and highinterference due to poor EMC characteristics. Furthermore, only the sendsignal is transmitted synchronously with the timing signal, whereasphase-synchronous transmission of the receive signal becomesincreasingly more difficult as a result of the internal delay times inthe slave at high data rates and may cause errors in the datatransmission.

When the SPI interface is used in a daisy-chain topology, that is, aring topology, very high latency times occur, which is why it is notpossible for that form to be used efficiently in automotive controlunits nowadays.

A method for implementing communication in a ring bus is further knownfrom British patent document GB 2 188 216 A. The communications sentbetween participants of the ring bus have what are commonly referred toas headers which comprise a plurality of digits indicating theavailability of the ring bus. In addition, a shift register is providedwhose maximum delay represents a number of bits in the header, a controldevice being able to manipulate data in the header of a message.

A method for transmitting a token in a communication ring is describedin German patent document DE 37 88 604 T2. In that instance, a prioritylevel of that token in a communication ring with a plurality of stationsis updated. It is provided that each respective range corresponds topriority levels of packets that need to be transmitted by eachrespective station, the token of the communication ring beingtransmitted from a first station of the communication ring as soon as afirst station transmits a frame containing a packet that is to betransmitted.

There are known from German patent document DE 198 03 686 A1 a methodand an apparatus for communication among, for example, equal-accessstations of a ring-shaped, serial fiber-optical bus. In that instance,time-cyclical container telegrams are generated, addressed and providedto the serial bus by the stations.

SUMMARY OF THE INVENTION

Against that background, a method and a communications arrangementhaving the features of the independent patent claims are presented.Further embodiments of the present invention will be apparent from thedependent patent claims and from the detailed description.

In the method, a serial connection is made of participants and hence ofnodes of a serial communications arrangement of ring-shapedconfiguration. In that arrangement, data transmission may take placefrom participant to participant with a delay of at least one bitduration, whereby data packets, which may contain messages, may betransmitted between the participants with very little latency. Thedescribed communications arrangement is formed in embodiment as asynchronous, bidirectional communications system or synchronous,bidirectional communications arrangement, exchange of data taking placethrough a ring topology which is provided for an embodiment of thecommunications arrangement. There is transmitted with a data signal orwith a signal at least one data packet which includes timinginformation. The communications arrangement corresponds in an embodimentto a ring-shaped network in which the participants may be seriallyconnected to one another in a ring shape. Such a communicationsarrangement may also be referred to as a ring.

In that arrangement, uniform addresses may be allocated for allparticipants, for example “00 . . . 0”, that is to say, no configurationof the slaves is necessary. Each slave modifies, for example subtractsor adds, a fixed value from or to an address value of a received dataframe that includes a message. Usually, the position of all participantswithin the communications arrangement provided as slaves needs to beknown only to the participant provided as a master.

In one embodiment of the present invention, it may be provided thattransmission of a system time to an interface of the communicationsarrangement is performed by continuous data transmission, that is,continuous synchronization, by a timing recovery module in the slaves.In addition, after a fixed number of data bits, stuffing bits may beinserted, thereby making it possible to ensure timing recovery in theslaves. Instead of the stuffing bits, which serve only for timingrecovery, bits for checking parity may also be inserted. A suitablechoice of parity bits makes it possible to ensure that at least one edgechange is present in the bit stream within a specified period of time.Alternatively, other encoding methods from the related art may also beused for timing recovery.

The data frames or empty frames sent by the master and exchanged betweenthe participants are separated from one another by a specific sequenceof bits of what is commonly referred to as an inter-frame symbol. Sincethe data signal is typically transmitted in encoded form in order tomake timing recovery possible, the inter-frame symbol typicallycorresponds to a special “illegal” signal which does not correspond toany data bit string. In a further embodiment, the inter-frame symbol mayalso be in the form of a series of zeros or ones. By measuring theinter-frame symbol, that is, in this case a period of time without anedge change, that period of time being dependent upon the number ofzeros and/or ones, a slave is able to ascertain the speed of the datatransmission and carry out a rough timing recovery. By insertingstuffing bits or parity bits, an edge change is brought about in thedata packet after a given number of bits, thereby ensuring thatexclusively the inter-frame symbol has the maximum length of zeros orones and is therefore an unambiguous bit string for synchronizationpurposes.

Alternatively, an inter-frame symbol may also be any other bit stringknown to the slaves, which, for example, provides for spectral spreadingin the frequency domain.

Using the inter-frame symbol it is possible to ascertain inter alia thepolarity of the signal transmission. Thus, for example, the two linesbetween two participants may, in the case of differential transmission,be laid in accordance with an optimum configuration of the layout, forexample in order to avoid crossings in the conductor track routing ofthe communications connections, and on the printed circuit board may beconnected to the integrated circuits (ICs) with any desired polarity. Itis advantageous that, with a suitable choice of encoding, for example byMiller encoding or modified frequency modulation, the recovery of theinformation is sensitive only to the time position of the edges, that isto say, is not level-sensitive, as a result of which the polarity of thedata signal is in any case a matter of choice.

In order that information and/or interrupt requests may be received fromthe slaves when the master is idling, that is, when the master does nothave any messages to send, the master continuously sends what arereferred to as empty frames. By sending the empty frames, which are alsoreferred to as idle frames, polling of the slaves therefore takes place.Each slave is able to use an empty frame and transmit its data and/or atleast a request in the form of what is referred to as a “soft interrupt”and thus a software interrupt, for example of a second level interrupthandler (SLIH), that is, a control program for an interruption of asecond layer in accordance with the OSI layer model, to the master as aresponse to the polling. In addition, the interface of the master may beautomated to the extent that, by using suitable methods, the datadirectly received and/or the data to be retrieved at the slaves arewritten directly into the memory of the master.

The physical layer of the serial interface of a participant includespoint-to-point connections in simplex mode, in which transfer of datatakes place in one direction only. Those connections may be electricallyasymmetrical, for example via CMOS level, electrically symmetrical, forexample via differential LVDS signal transmission or also optical.Furthermore, transmission may also be carried out with the aid of amodulation method, for example for multiple use of signal and/or supplylines.

In further embodiment, the method permits the regeneration of the signalin each slave, so that the signal only has to cross a short distance ineach case. In that manner, the technical expenditure is additionallyreduced despite the high transfer rate.

Furthermore, the method typically allows any desired number of slaves tobe connected to the arrangement. The number of slaves is limited by theaddress space and thus by the size of the address field. The adding offurther slaves has no effect on the electrical characteristics, forexample signal quality, or the EMC behavior, in other words theelectromagnetic compatibility of the communications arrangement.

The method makes it possible to ensure implicitly that all slaves arecapable of operating for communication and supplying timing, at leastwith regard to their interface.

In advantageous embodiment, provision may be made for data transmissionbetween a microcontroller and an application-specific integrated circuit(ASIC) within a device for a motor vehicle provided as an automotivecontrol unit. A serial interface for at least one participant, which inthis case corresponds to a device and/or is associated with such adevice, is defined within the scope of the exemplary embodiments and/orexemplary methods of the present invention. With that interface, it ispossible to carry out at least individual steps of the described method.Usually, the described communications arrangement and the describedmethod may be used for devices and hence for participants in differentelectromechanical apparatuses if transmission of data is envisaged forthem.

In an embodiment for a communications arrangement having, for example, aring structure, an addressing concept for participants is provided bythe exemplary embodiments and/or exemplary methods of the presentinvention, wherein when a data packet is forwarded from one participantto the next participant, a delay, of at least one bit duration, takesplace.

It is thus possible to provide with the exemplary embodiments and/orexemplary methods of the present invention a communications arrangementand a method for serial data transmission between participants which maybe in the form of logic components within a control unit. Participantsare provided in the form of at least one discrete logic component (ASIC)as slaves, and one logic component (microcontroller) as master for thecontrol, that is, for the closed-loop and/or open-loop control, of atleast one slave. Simple and inexpensive implementation in logiccomponents, that is, microcontrollers and/or ASICs, with high data ratesis made possible, it being possible to achieve such implementation usingfew connection lines on a printed circuit board and with few pins of thelogic component, that is to say with low costs in terms of layout andconnection technology. Furthermore, the method is able to make possiblethe transmission of higher data rates than in the case of the SPIinterface typical for automotive applications. The timing signal encodedin the data signal guarantees phase-synchronous transmissionindependently of the line routing and the delay times.

The participants are usually arranged in the communications arrangementin the form of a ring topology, whereby it is possible for theparticipants to be connected by point-to-point connections using aminimal number of pins. In a ring topology, the slowest participantdetermines the bus speed. Where appropriate, combination or grouping ofparticipants in different rings may be performed, in which case anembodiment of the method according to the present invention may becarried out in each of those rings as a self-contained embodiment of acommunications arrangement according to the present invention. If aplurality of functional groups are integrated in one control unit, forexample if a microcontroller communicates with at least one ASIC ofdifferent functional units, each of the respective functional groupstypically makes use of a separate ring arrangement.

The microcontroller normally acts as the master, as a result of which nobus arbitration is required. Thus, in accordance with the present-daySPI protocol, which is also a master-slave concept, the master is ableto cyclically interrogate the slaves by what is commonly referred to aspolling.

In accordance with the SPI standard, it is possible for synchronous datatransmission to take place. No separate lines are required, however, fordata and timing. The interface provided provides for encodedtransmission of the timing within the data signal, for example 8B/10Bencoding, Manchester encoding or Miller encoding, that is to say,modified frequency modulation. Consequently, for low data rates only twopins are provided per participant, with one line to the precedingparticipant and one line to the subsequent participant. High data ratesprovide for differential transmission with four pins per participant,with two lines to the preceding participant and two lines to thesubsequent participant. Apart from providing a reduction in costs,encoded transmission of the timing information may also make it possiblefor no delays to occur between timing and data over a transmission pathbetween the participants. A system time is specified by the master andall slaves synchronize themselves using their own, local timing recoverymodules, for example by a phase-control loop or by oversampling withcorresponding synchronization with the message signal.

During initialization at the beginning of a transmission, starting froma first interface, from which data packets are sent, the master sends asynchronization signal to the first slave in the communicationsarrangement configured, for example, as a ring. As soon as the systemtime of the first slave, that is, the receiver, is in phase with themaster, forwarding of the synchronization signal to the next slavebegins. In this operation, passing of data packets between interfaces ofadjacent participants takes place. That procedure continues throughoutthe entire communications arrangement. Once synchronization of all theslaves in the communications arrangement configured, for example, as aring has taken place, a receiver in the master, usually a secondinterface with which data packets are received, may also be adapted.Owing to the delay, unknown in the master, upon transmission of dataframes or empty frames through the ring and owing to the associatedphase offset from its own system time, in a last step of theinitialization procedure phase correction is carried out also in themaster. Once the phase in the receiver of the master has also beencorrected, all of the participants are in phase and are then able totransmit data packets synchronously.

To avoid frequency fluctuations of the timing recovery modules in theslaves due to constant re-synchronization, continuous transmission ofdata and hence of data packets in what is referred to as continuous modemay be employed. That first of all eliminates the backlog forsynchronization patterns at the beginning of a data packet which isrequired in the case of packet-oriented transmission (so-called bursttransmission mode) as opposed to continuous transmission (so-calledcontinuous transmission mode). Owing to the possibility of continuoussynchronization, the slaves also do not require any further system timeas generally has to be additionally supplied besides the communicationsinterface in the case of known systems. Consequently, a saving may bemade in further lines and pins. Continuous mode optionally provides forthe use of a spread-spectrum technique, in other words a spectralspreading for improvement of the EMC characteristics. Furthermore, useof packet-oriented transmission (so-called burst transmission mode) isalso possible, although that possibly necessitates an additional linefor transmission of the system time from the master to the slaves.

In further embodiment, the participants participating in thecommunication have shift registers. Automatic timing of the shiftregisters occurs in this case, it being possible by using a timingrecovery module to recover a timing for the time base of the masterprovided as a microcontroller. The shift register automaticallytransmits the data with a timing signal of that timing. Since the bitsmay be processed individually, it is possible to achieve the minimumlatency time of one bit duration per participant. Latency times, whichoccur until a data packet with a message has been transmitted throughthe ring, are therefore small, thereby making it possible to ensure thereal-time capability of the communications arrangement. Owing to theminimal delay of the message by at least one clock cycle, signalconditioning, that is to say, bit-reshaping, which may have alevel-related and/or time-related effect, also takes place in eachparticipant.

Within the scope of the exemplary embodiments and/or exemplary methodsof the present invention, addressing of the participants is carried outnot by way of a separate select signal, but by addressing within a datapacket in the form of a data frame or an empty frame. In order for theaddress field to be detected in the continuous data stream, theinter-frame symbol, which corresponds in form to a start symbol and anend symbol of a data packet, is inserted.

The inter-frame symbol may also be regarded as the preamble of a dataframe, with which the slaves are able to synchronize themselves with theforthcoming data. In that manner, a synchronization of the frame takesplace, since every participant knows that data are always transmittedafter the inter-frame symbol. The inter-frame symbol may also be used toimplement variable data lengths.

The master may address the slaves by the addressing procedure and maywrite or read data by using appropriate commands. By using a reservationflag, that is to say, a bit value, it is possible to signal directlyafter the inter-frame symbol whether the frame is occupied by usefuldata and only the participant addressed is allowed to process the dataframe. That dedicated bit is usually referred to as a reservation flag,that reservation flag signaling whether the data packet contains a dataframe or an empty frame.

In one possible embodiment of the present invention, each slave adds orsubtracts a fixed value to or from an address value of the address of areceived data packet. In that operation, on addressing of a participant,the ring topology of the communications arrangement, which may beprovided as a ring-shaped network, is used in such a way that eachparticipant adds or subtracts “1” to or from the current address,whereby in the case of an address “000 . . . 0” containing only zeros adesired participant may be addressed. In one embodiment of the method,all the participants, usually all the slaves, are sensitive to anidentical address. That subtraction or addition typically takes placeonly when the data frame contains useful data, that is to say, when thereservation flag after the inter-frame symbol has been set. This isusually implemented by a 1-bit subtractor by transmitting the addressLSB-First, that is, the address of the first least significant bit.

If an address value of a received address is “000 . . . 0”, the datathat follow are intended for the current slave and are processed by it.In addition, by the described procedure, that is, subtraction by “1”,the address value of the address field in the data frame isautomatically set by an overflow to “111 . . . 1”, which ensures thatthat data packet is passed on as a message as far as the master and, forexample, may contain an acknowledge of the correct receipt of themessage or directly a response. That data packet is forwarded to thenext participant within the communications arrangement. In thatoperation, a modification, for example a subtraction or addition, iscarried out for the re-set address value by all subsequent slaves. Byautomatic setting of the address value in the address field of the dataframe to the highest value in the slave, the master is able to tracewhich slave the message was sent from since, owing to the structure ofthe address value, the master is able to trace how many modifications oralterations were carried out for the set address value, the number ofmodifications carried out corresponding to the number of slaves thathave received and forwarded the data packet after setting of the addressvalue by a slave.

Using the described interface, it is possible to switch betweendifferent frame lengths. If a fixed frame length is selected, small datapackets may sometimes be transmitted in a large frame. In that case,padding of the data frame with dummy data is necessary. It is equallypossible to implement a variable frame length, in which case the lengthof the shift registers in the slaves may be independent of one anothersince the irrelevant data frames are merely passed on in each case.

In the case of variable frame lengths, by using an empty frame theslaves are able to signal to the master a request that useful data areto be transmitted from the slave, after which those data are thenfetched by the master by sending a data frame of appropriate length.

If data are to be passed from the slave to the master without a requestfrom the master, the slave is able to fill an empty frame sent by themaster. For this, a bit after the inter-frame symbol, a so-calledreservation flag, is set. The address value in the address field of thedata frame is usually set by the slave filling the empty frame to thehighest value (“111 . . . 1”). This can be done in such a way that theaddress value in the empty frame is set by the slave to “111 . . . 1”and is communicated to the master by subtraction or addition of theaddress in the address field of the data frame in each slave. Setting ofthe address to the value “111 . . . 1” may be carried out, for example,by an OR operation by overwriting all the address bits with a “1”. Inthat case also, the master is able to trace, on the basis of the numberof modifications of the address field carried out by slaves, which slavehas filled the empty frame and re set the address value for the addressfield. With that form of implementation, on being sent by the master theaddress field in the data frame or empty frame may contain random data,whereby spectral spreading may take place and hence better EMCcharacteristics may be obtained. In a further embodiment of theinterface, an empty frame may also contain a useful data field, whichenables a slave to directly transmit data not exceeding the data lengthspecified by the empty frame.

If the configuration of the empty frames does not contain a useful datafield, the slave is only able to send an interrupt, for example a softinterrupt, to the master and wait for the master to send a suitable dataframe to the slave in the next cycle. That data frame is provided with aset reservation flag and the address of the slave. The contents of thedata frame may then include, for example, once more the command to readout a register, after which the slave subsequently copies the availableinformation into the data frame or, especially, into the empty frame.If, however, an empty frame has a useful data field, the slave is abledirectly to attach the data to be transmitted, provided that the data donot exceed the length of the data field of the empty frame.

In order to trigger signaling in the case of this variant of thecommunication, prioritization of a slave is carried out on the basis ofthe position of the slave in the communications arrangement. In oneconfiguration of the interface, a slave is able to communicate signalingto the master by setting a bit that has been allocated to it. Hence,this constraint may, however, lead to severe restrictions in terms ofthe layout of the printed circuit board. To avoid this, according to thenumber of slaves as participants in the communications arrangement, anumber of bits that is at least as great as the number of participants,normally the number of slaves, in the communications arrangement thatare capable of triggering an interrupt follows the inter-frame symboland the reservation flag. Participants that only receive data from themaster and do not supply messages to it, therefore, do not have aninterrupt capability and consequently they ignore the empty frames.Accordingly, for this type of participant, it is also not necessary foran interrupt bit to be provided in the empty frame. If an interrupt isto be triggered by an interrupt-capable participant, that participantsets the bit that has been allocated to it. Prioritization of thehandling of the interrupt may then be carried out in the master(microcontroller).

A variant in which allocation of a fixed bit is provided requiresknowledge in the slave of its position in the communications arrangementand/or knowledge of a bit allocated to it in an empty frame. In anotherconfiguration of the interface, no fixed bit is allocated to a slave.Instead, the bit string of the empty frame after the reservation flag isshifted by one position by each slave and a new bit is inserted. In thisinstance, the information of the last bit is lost in each case. Thatdoes not represent a limitation, however, since at the beginning of thetransmission, that is to say, the sending of the empty frame by themaster, an empty frame does not carry any information and the number ofbits provided therein is at least as great as the number of slaves ofthe communications arrangement that are capable of dispatching aninterrupt request. If an interrupt request or an indicator forforthcoming data is to be triggered, the bit inserted by the slave maybe set. Thus, an identical algorithm is stored in every slave and, byknowledge of the position of the participants in the communicationsarrangement, the master is able to attribute the interrupt requestsaccordingly and process them in accordance with the desiredprioritization.

In a further configuration, it is possible for error correction also tobe added. If a communications arrangement is configured in a ring shape,by virtue of the ring topology it may be laid out in such a manner that,after the transmission through the ring, the master compares thereceived message with the message that it originally sent and is thusable to deduce whether a transmission was error-free or containederrors. As a rule, the response to a request is sent by the slavesdirectly to the master in order to afford better capacity utilization ofthe system. Alternatively, the slave may respond only with the next datapacket addressed to it, as corresponds to present-day configurations ofan SPI communication. Optionally, a cyclic redundancy check (CRC) may becarried out as a checksum process or a parity check in the data framemay be added and the receiving participant provides an acknowledge atthe end of its response. In addition, it is optionally possible to addparity bits also to the address field of the data frame.

If desired, transmission of the data may be carried out in such a mannerthat a message with data, which is usually provided in a data frame andtransmitted completely through the ring starting with the sender, thatis, the master, is decoded again in the master before the next dataframe is sent. Alternatively, a continuous bit stream of data may bechosen, that is to say, sending of the next data frame takes placedirectly afterward rather than only after the previous message has beenreceived. In this case, it is ensured in the protocol by arbitrationthat a soft interrupt of a slave is handled correctly in the event ofoverlapping addressing by the master, that is to say, when the masteraddresses the slave before the soft interrupt of the slave has beenprocessed. That scenario is permissible and has no effect on theconfiguration of the described bit transmission layer.

In the case of the continuous data stream, the length of the inter-framesymbol may also correspond, for example, to the number of participants,normally the number of slaves, of a communications arrangement providedas a ring shape. Owing to the delay per participant of typically one bitduration, the duration of the transmission through the ring thencorresponds exactly to the transmission time of an inter-frame symbol.The length of the inter-frame symbol or the time duration of the sendingof the inter-frame symbol is thus selected according to the delay timeof the transmission through the ring. Accordingly, a continuous datastream is provided, which, for example, has a positive effect on thesynchronization of the slaves. At the same time, the master is able todecode the message that is in circulation before sending the next dataframe. Accordingly, a rapid reaction to incoming soft interrupts ispossible, and no overlap occurs between the dispatching of an interruptrequest by the slave and reaction to a request by the master.

Optionally, an additional logic module is implemented in the master inorder to write received data, for example sensor data, directly into amemory. In addition, the polling of the slaves may be automated. Thatresults in a reduction in software interaction, which relieves theburden on the central processing unit (CPU). In addition, the registersof the ASICs (slaves) may be filed transparently in the memory of themicrocontroller (master). Possible HW modules are known from the relatedart in the form of DMA, transfer units or also message boxes.

In addition to the spread-spectrum techniques already mentioned, thereis the option of using a block-synchronized scrambler. In the case ofthe block-synchronized scrambler, the same m-sequence is simultaneouslymodulo-2-added to the data in the sending and receiving participants.

An interface provided within the scope of the present invention for aparticipant may be used for applications in the automotive sector. Inconformity with the known standards such as IIC (inter-integratedcircuit) and SPI (serial peripheral interface), the mentioned interfacemay also be used universally and accordingly is not restricted to use inthe automotive sector or even in control units (ECUs).

The communications arrangement according to the present invention isconfigured to carry out all the steps of the method presented. It isalso possible for individual steps of that method to be carried out byindividual components, usually by participants, of the communicationsarrangement. In addition, functions of the communications arrangement orfunctions of individual components of the communications arrangement maybe implemented as steps of the method. Furthermore, it is possible forsteps of the method to be implemented as functions of at least onecomponent of the communications arrangement or of the entirecommunications arrangement.

Further advantages and embodiments of the exemplary embodiments and/orexemplary methods of the present invention will be apparent from thedetailed description and the accompanying drawings.

It will be appreciated that the features mentioned above and thefeatures yet to be described hereinafter may be used not only in therespective combination indicated but also in other combinations or inisolation, without departing from the scope of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic illustration of an embodiment of acommunications arrangement according to the present invention.

FIG. 2 shows a schematic illustration of an example of a structure of adata packet with a data frame as used in one embodiment of the methodaccording to the present invention.

FIG. 3A shows a schematic illustration of a data packet which has afirst variant of a frame in the form of an empty frame.

FIG. 3B shows a schematic illustration of a data packet which has asecond variant of a frame in the form of an empty frame.

FIG. 3B shows a schematic illustration of a data packet which has athird variant of a frame in the form of an empty frame.

FIG. 3D shows a schematic illustration of a data packet which has afourth variant of a frame in the form of an empty frame.

FIG. 4 shows a flow diagram relating to a further embodiment of themethod according to the present invention, wherein processing of anaddressing of a slave takes place.

FIG. 5 shows schematically a block diagram of a block-synchronizedscrambler as used in a further embodiment of the method according to thepresent invention.

DETAILED DESCRIPTION

The present invention is illustrated schematically in the drawings withreference to embodiments and will be described in detail hereinafterwith reference to the drawings.

The Figures are described in a continuous and overlapping manner;identical reference numerals denote identical components.

The embodiment of a communications arrangement 2 illustratedschematically in FIG. 1 is of a ring-shaped configuration and includes aplurality of participants connected in series, namely a master 4, afirst slave 6, a second slave 8 and an n-th slave 10 connected to oneanother by sections 12 of a line. The master further includes a firstdigital serial interface 14 for sending data packets, with which master4 is connected, depending on definition, to a beginning or an end of theline. In addition, master 4 includes a second digital serial interface16 for receiving data packets, with which master 4 is connected,depending on definition, to a beginning or an end of the line. Serialfirst interface 14 is connected in this case to a system clock 18.Serial second interface 16 is connected to a module for detection ofphase position 20 (commonly referred to as a delay locked loop).Furthermore, only master 4 is connected to a quartz oscillator 22.

Each of slaves 6, 8, 10 has a digital serial interface provided as aslave interface 24, each of which interfaces is connected to twoconnections 12 and hence to one data line. Thus, a connection existsbetween two participants. In addition, each serial slave interface 24 isconnected to a timing recovery module 21 from which a local system time19 may be derived.

To provide communication between the participants of communicationsarrangement 2, in one embodiment of the invention it is provided that,starting at a start interface 14 of master 4, messages are continuouslytransmitted as data packets via a bit stream 26 from serial slaveinterface 24 to serial slave interface 24 of slaves 6, 8, 10. When adata packet has reached a last slave 6, 8, 10, in this case the n-thslave 10, the data packet is passed from slave interface 24 of lastslave 10 to end interface 16 of master 4.

In the case of communications arrangement 2 in a ring topology, aplurality of slaves 6, 8, 10, in this case ASICs, with an identicallocal address are each serially connected via digital slave interface 24to master 4 which in this case is in the form of a microcontroller. Inthis embodiment, only master 4 has knowledge of the position of eachslave 6, 8, 10 in ring-shaped communications arrangement 2.

In one embodiment of the present invention, a participant or node of thering-topology communications arrangement provided as a slave 6, 8, 10 isformed in such a manner that each slave 6, 8, 10 modifies an addressvalue of a received address, typically an address value in an addressfield of a data frame provided for passing a message to at least oneslave, by a fixed value and forwards it to the next participant. In thatoperation, the address value may, for example, be subtracted by thefixed value “1”. Such an alteration of an address value may inembodiment also be performed for other data packets, this also beingpossible when such data packets do not include a data frame, but includeonly an empty frame with a message.

An encoding method for recovering timing information from a data signalof a data packet is carried out in such a manner that, by equidistantinsertion of a parity bit, it is ensured that at least one edge changeis present in bit stream 26 within a specified period of time. Bycontinuous data transmission it is possible to ensure synchronization ofslaves 6, 8, 10 in communications arrangement 2. It is also possible forother suitable encoding methods to be applied.

The data packet is passed from master 4 to first slave 6 and insuccession from slave 6 to slave 8 as far as last slave 10 and from lastslave 10 to master 4. The data packet accordingly passes through all theparticipants of communications arrangement 2. The data frame with whicha message is to be passed to at least one slave 6, 8, 10 has an addressfield with an address. It is provided that each slave alters an addressvalue of the received data frame containing the message to betransmitted by a fixed value, for example by subtraction or addition,and forwards it to the next participant. In that operation, the addressvalue is altered by each slave in the same manner, depending on thealgorithm specified for this. Within the communications arrangement 2shown, slaves 6, 8, 10 have identical local addresses. In addition, anidentical algorithm for the communications interface is stored in allthe slaves. Typically, only the module for inter-chip communication isidentical and otherwise the participants may very well include differentfunctions.

The data frames and empty frames described below are merely illustrativeembodiments. It is possible to position further bits between the datablocks or also to transpose the arrangement of the blocks within a dataframe.

An example of a data packet 30 shown in FIG. 2, which is transmitted inone embodiment of the method according to the present invention,includes at a start a first inter-frame symbol (IFS) 32 and at the end asecond inter-frame symbol 34. Between those two inter-frame symbols 32,34, which are typically identical, a data frame 36 is arranged withindata packet 30. At the start of data frame 36, it has immediately afterfirst inter-frame symbol 32 a reservation flag 38 which providesinformation on the type of data packet 30 in circulation. In FIG. 2, itis provided in embodiment that reservation flag 38 has, for example, thevalue “0” and therefore the frame is in the form of a data frame 36.After reservation flag 38, data frame 36 includes an address field 40with an address value for an address. Data frame 36 further includes anactual message 42 which may include instructions and data, in the formof useful data in this case, and also further checksums and parity bits.

FIG. 3 a is a schematic illustration of a further example of a datapacket 50, which in this case has a first variant of a frame in the formof an empty frame 52. That data packet 50 also starts with a firstinter-frame symbol 32 and ends with a second inter-frame symbol 34.Between the two inter-frame symbols 32, 34, there is an empty frame 52in which, in contrast to first data packet 30 with data frame 36, areservation flag 54 has the value “1” and thus classifies the frame asan empty frame 52. In addition, that empty frame 52 also includes anaddress field 43 with an address value. The embodiment of empty frame 52shown here and hence data packet 50 does not, however, have a messageand therefore has no useful data.

Using data packets 50 illustrated in FIG. 3 a, the master continuouslysends empty frames 52 to the slaves to carry out polling. Each slave mayinsert data into such a data packet 50 and/or send at least one request(soft interrupt) to the master. This is typically done in a form suchthat the slave inverts reservation flag 54, usually a reservation bit,and sets the address value to “111 . . . 1”. By activation ofreservation flag 54, the frame is then blocked for the subsequentparticipants analogously to a data frame. Each subsequent participantalso modifies the address value by a fixed data value, analogously tothe procedure in the case of a data frame of FIG. 2. Data packet 50 isconsequently passed on through to the master, the master being able tocalculate back, by reference to the address information, which slave hasmade an interrupt request.

The third example of a data packet 56 illustrated schematically in FIG.3 b also includes a first inter-frame symbol 32 and, at the end, asecond inter-frame symbol 34. That data packet 56 further includes aframe, which in this case is in the form of a second variant of an emptyframe 58. That empty frame 58 includes a reservation flag 54 with thevalue “1” which defines that frame as an empty frame 58. Empty frame 58further includes an address field 43 with an address and also a message60 which in this case includes data in the form of useful data.

That empty frame 58 may be filled by a slave with data for passinginformation to the master, in which case reservation flag 54 is set. Theaddress value of an address of address field 43 in empty frame 58 is setto a maximum value “111 . . . 1”. This may be done in such a manner thatthe address value in empty frame 58 is set by the slave to “111 . . . 1”and passed to the master by subtraction or addition of the address inthe address field of the data frame in every subsequent slave. Settingof the address to the value “111 . . . 1” may, for example, be performedby an OR operation by overwriting all address bits with a “1”, it beingpossible for address field 43 of empty frame 58 to contain random data.Via the message, direct transmission of useful data not exceeding a datalength defined by empty frame 58 is made possible for the slave. Thenumber of modifications carried out on the set address value of theaddress corresponds to the number of subsequent slaves. Thus, the masteris able to determine which slave has filled empty frame 58 with data andre-set address field 43.

The fourth example of a data packet 62 shown in FIG. 3 c includes, inaddition to first inter-frame symbol 32 and second inter-frame symbol34, a frame in the form of an empty frame 64, which in this case is inthe form of a third variant of an empty frame 64. In this case also, thetype of frame is defined as an empty frame 64 by a reservation flag 54,which in this case has the value “1”. Empty frame 64 further includes asa further bit a first interrupt bit 66, which is allocated to a firstslave, a second interrupt bit 68, which is allocated to a second slave,a third interrupt bit 70, which is allocated to a third slave, and ann-th interrupt bit 72, which is assigned to an n-th slave.

Accordingly, in data packet 62, the bit provided as interrupt bit 66,68, 70 follows inter-frame symbol 32 and reservation flag 54 for everyslave of the communications arrangement. If an interrupt is to betriggered by a slave, that slave triggers interrupt bit 66, 68, 70, 72allocated to it. In this configuration, a sequence of interrupt bits 66,68, 70, 72 corresponds to a sequence of slaves along the communicationsarrangement, but the sequence of the interrupt bits does not necessarilyhave to be tied to the sequence along the communications arrangement.

The embodiment shown in FIG. 3 d for a fifth example of a data packet 74also begins with a first inter-frame symbol 32 and ends with a secondinter-frame symbol 34. The data packet also includes a reservation flag54, which in this case has a value “1”, which defines a frame of thatdata packet 74 as an empty frame 76. In addition, empty frame 76includes as further bits a variable number of interrupt bits 80, 82, 84,more specifically an n−1-th interrupt bit 80 for an n−1-th slave and afirst interrupt bit 82 for a first slave of a communicationsarrangement. FIG. 3 d also shows an additional n-th interrupt bit 78 tobe inserted for an n th slave. This variant of the empty frame furtherincludes an x-th interrupt bit 84.

A shifting of interrupt bits 80, 82, 84 within empty frame 76 afterinsertion of n-th interrupt bit 78 into empty frame 76 by an n-th slaveis indicated here by arrow 86. Thus, within empty frame 76, a sequenceof interrupt bits 78, 80, 82, 84 after reservation flag 54 may beshifted by one position by every slave and a new interrupt bit 78 may beinserted by every slave. Empty frame 76 that was originally sent by themaster does not include useful data. A number of provided interrupt bits78, 80, 82, 84 is greater than or equal to the number ofinterrupt-capable slaves in the communications arrangement. If aninterrupt is to be triggered, it may be set by n-th interrupt bit 78inserted by the n-th slave. If no interrupt is to be triggered, a bit isalso inserted, but it is not then set. The number of interrupt bitsprovided could in principle be smaller than the number of slaves in thecommunications arrangement, but then not every slave is capable ofsetting an interrupt bit. In that case, the communications modules ofthe connected slaves must be designed differently or at least configureddifferently, which is not an optimal solution.

The embodiments shown in FIGS. 2, 3 a and 3 b for data packets 30, 50,56 each have an address field 40, 43 via the structure of which, usuallya structure of the address value, a data packet 30, 50, 56 may beaddressed by master 4 to an i-th slave 6, 8, 10 or by i-th slave 6, 8,10 to master 4 of the embodiment of communications arrangement 2illustrated in FIG. 1.

The mentioned structure of address field 40, 43 has in one configurationN bits. The maximum binary numeric value capable of being represented bythe N bits must be greater than or equal to the number of participants,typically greater than or equal to the number n of slaves 6, 8, 10. Inone embodiment of the method according to the present invention, it isprovided that a sent data packet 30, 50, 56 is directed to the i-thslave 6, 8, 10, the address field being provided by master 4 with thebinary number i.

That data packet 30, 50, 56 is sent by master 4 to slaves 6, 8, 10, eachslave 6, 8, 10 up to the i-th slave 6, 8, 10 through which the datapacket passes modifying the address value in the address field of thedata frame by a fixed value, for example by the value “1”, for exampleby subtraction. If no overflow occurs on subtraction, the address valuewas other than “00 . . . 0” and it is thereby signaled to slave 6, 8, 10performing the examination that data packet 30, 50, 56 is not intendedfor it. As soon as i th slave 6, 8, 10 is reached, the mentionedoverflow occurs and i-th slave 6, 8, 10 recognizes that the receiveddata frame may be processed, that is to say, as a rule that the contentsof data packet 30, 50, 56, for example a message 42, 60, are intendedfor that i-th slave 6, 8, 10.

In an alternative configuration of the interface, the address value hasin one configuration n bits. Thus, one bit of the address value isprovided for each of the n slaves 6, 8, 10. If it is provided in oneembodiment of the method according to the present invention that a sentdata packet 30, 50, 56 is directed to i-th slave 6, 8, 10, the i-thleast significant bits of the address value are set in each case bymaster 4, and n−i-th most significant bits are not set. Alternatively,the i-th most significant bits may be set and the n−i-th leastsignificant bits not set.

That data packet 30, 50, 56 is sent by master 4 to slaves 6, 8, 10, eachslave 6, 8, 10 up to i-th slave 6, 8, 10 through which data packet 30,50, 56 passes clearing and thus modifying a set bit in each case. Whendata frame 36 arrives at i-th slave 6, 8, 10, all the bits are cleared,that is, not set, and thus it is signaled to i-th slave 6, 8, 10 thatdata packet 30, 50, 56, as a rule the contents of data packet 30, 50,56, for example a message 42, 60, are intended for that i-th slave 6, 8,10.

Accordingly, i-th slave 6, 8, 10 for which data packet 30, 50, 56 isprovided or intended produces an overflow for the address value. Theoverflow and/or an address value structure produced by the overflowsignals to i-th slave 6, 8, 10 that data packet 30, 50, 56 is directedto it. Before forwarding of data packet 30, 50, 56 to a subsequentparticipant of the communications arrangement, that is, to at least oneslave 6, 8, 10 or, where applicable, to master 4, all N bits of theaddress value of address field 40, 43 are set by that i-th slave 6, 8,10 to the same value, for example all bits are set to “1” or all bitsare set to “0”. The subsequent n-i slaves 6, 8, 10 modify the re-setaddress value of address field 40, 43 in exactly the same way as theother i slaves 6, 8, 10 that have already received data packet 30, 50,56. Thus, the re-set address value is modified n−i times. Master 4,which receives that data packet 30, 50, 56 again, is able to recognizeon the basis of the structure of the address value, that is, on thebasis of the number of modified bits, that the address value has beenmodified n−i times. That indicates to master 4 that data packet 30, 50,56 has been processed by i-th slave 6, 8, 10.

If an i-th slave 6, 8, 10 provides an empty frame 52, 58 of data packet50, 56 with information for master 4, that i-th slave 6, 8, 10 alsore-sets the address value of address field 43. In this case also, assoon as master 4 receives data packet 50, 56 with the informationprovided for it, it is able to recognize on the basis of the structureof the address value that the data packet was modified by the n−isubsequent slaves 6, 8, 10 n−i times and that the information originatesfrom i-th slave 6, 8, 10.

Reservation flag 38, 54, which may also be referred to as a token,defines whether a data packet 30, 50, 56, 62, 74 has a data frame 36(reservation flag=“0”) or an empty frame 52, 58, 64, 76 (reservationflag=“1”). Depending on definition, the bit value of reservation flag38, 54 may also be reversed. It is possible to regard a set or not setreservation flag 38, 54 as an allocated or free reservation flag,respectively.

Communication arrangement 2 of FIG. 1 may be formed in a motor vehiclefor transmission of data packets 30, 50, 56, 62, 74 between amicrocontroller and ASICs in a control unit of the motor vehicle, thecontrol unit having the participants of communications arrangement 2.

A protocol for priority control of the communications arrangement issuch that each slave is able to transmit a request (soft interrupt) tothe master, which is described herein with reference to FIGS. 3 a, 3 b,3 c and 3 d. Thus, an identical algorithm of the communicationsinterface is stored in each slave and the master is able, on the basisof knowledge of the position of the participants in the form of slaves,to attribute the interrupts accordingly and, in the case of the possibletransmission of a plurality of interrupt requests in one data packet asshown in FIGS. 3 c and 3 d, is able to process the interrupts inaccordance with a desired prioritization. With a protocol for prioritycontrol it is possible for a request to be transmitted to the masterfrom at least one slave using a data packet including an empty frame.

Encoding for recovery of timing information from a signal may be carriedout in such a manner that a parity bit is inserted equidistantly in thedata frame, so that the transmitted bit stream has at least one edgechange within a specified period of time.

In order that information may be received from the slaves in the idlestate of the master, the master continuously sends empty frames in orderto carry out polling of the slaves. Each slave may provide an emptyframe with data and transmit those data and/or at least a request in theform of what is commonly referred to as a “soft interrupt” and thus asoftware interrupt, for example of a second-level interrupt handler(SLIH), that is, a control program for interrupting a second layer inaccordance with the OSI layer model, to the master as a response to thepolling.

The flow diagram shown in FIG. 4 shows an example of processing of anaddress value of an address in the address field of a data frame whichis sent by a master, through n slaves as participants within acommunications arrangement, for example a ring-shaped communicationsarrangement, in a further embodiment of the method according to thepresent invention. In this case, implementation of addressing takesplace during the data transmission within each slave in the ring.

In addition, receipt of an incoming data packet is detected by adetection 90 of the inter-frame symbol. Thereafter a check 92 checkswhether a reservation flag of a frame of the data packet has either thevalue 0 or the value 1.

If the reservation flag is not set, the received data packet includes avariant of an empty frame. In that case, an interrupt 94 and thus arequest and/or an inquiry to the master may, if required, be triggeredby an i-th slave. Thus, the i-th slave is given the opportunity toprovide the received data packet with a message which is forwarded tothe master.

Alternatively, the reservation flag is set, and therefore the datapacket includes a data frame. In that case, processing or modificationof the address field takes place. This address value ADDR [1 . . . N]has in this configuration N bits or places. In this instance, themaximum binary number consisting of N bits corresponds to the number nof slaves in the communications arrangement.

To modify the address field, in step 96 a variable i is provided withthe value “1”.

Thereafter, inversion 98 of the first address bit ADDR[1] of the addressfield ADDR [1 . . . N] of a received data frame takes place. Owing tothe address being transmitted with the beginning of the leastsignificant bit, inversion of ADDR[1] corresponds to the subtraction of“1” from the address value.

In next step 100 of the processing, the result of inversion 98 to thevalue “1” is checked. If the value ADDR[1] is not “1”, that is, if thevalue is “0”, no overflow occurred upon subtraction. In that case, theslave forwards the data packet with the now modified address to the nexti+1-th slave. Since no processing is further required by the slave, inaccordance with the method it waits for the new detection 90 of aninter-frame symbol and forwards unchanged the bits that have meanwhilebeen received.

If it is found in the check in step 100 that ADDR[1] has the value “1”,an overflow occurred upon subtraction. The slave then has to check instep 102 whether the complete address field of length N has already beenrun through. If that is not the case, the variable i is incremented bythe value “1” (step 104). Then, inversion 98 of the next highersignificant bit takes place.

The loop is repeated for the subsequent bits of the address field untilan inverted address bit provides a “0”. If no overflow has thenoccurred, that is, if the complete address field has not yet been runthrough, it is signaled to the slave that the received data packet wasnot intended for it and the slave branches back to step 90 and waits forthe next incoming inter-frame symbol in order to proceed with possibleprocessing of the next data packet. If, however, an overflow occurs andall positions of the address field are therefore set, that is, have a“11 . . . 1”, that signals to the slave that the data packet is intendedfor it and has to be processed by it. In that case, the polling in step102 takes effect, according to which the variable i then corresponds tothe value 2N−1 (maximum representable value of N bits), according towhich all bits of the address field have now been inverted. The resultof the evaluation of the address field is step 106 in which it isascertained that the frame of received data packet 30 is a data frame 36and is intended for the i-th slave receiving that data frame 36 withindata packet 30. Subsequently, evaluation of the instructions withinmessage 42 and processing of the data of message 42 are carried out bythe i th slave.

The steps shown in the flow diagram may be carried out, for example, bya counter, an inverter and with comparators as components of aninterface of a slave and/or of the slave. In the illustrated embodimentof the method, the subtrahend was set with “1”. Other ways ofimplementing subtraction or addition and thus other ways of modifyingthe address with other fixed values are usually also possible.

FIG. 5 shows a block diagram for an embodiment of a block-synchronizedscrambler 110. Scrambler 110 includes a first m-sequence generator 112which is arranged in master 114 (μC) as sending participant, and nm-sequence generators 116, only an i-th m-sequence generator in an i-thslave 118 (ASIC) being illustrated here. Between master 114 and the nslaves 118, an encoded transmission 120 of data packets takes placewithin a bit stream 122. In this case, transmission path 120 may containfurther participants. Furthermore, it is also possible that, in eachslave, the message is first decoded by an m-sequence generator 116 andthen re-encoded with a further, possibly different, m-sequence generator112, that is to say, transmission path 120 between two participants isencoded in each case. In that case, transmission path 120 does notcontain further participants. Furthermore, it is also possible that onlyselected parts of the bit stream, typically the useful data, arescrambled.

In addition to the possibilities of spectral spreading alreadymentioned, there is also the option of using block-synchronizedscrambler 110. In the case of block-synchronized scrambler 110, the samem-sequence is simultaneously modulo-2-added to the data in the sendingparticipant, in this case master 114, and to the receiving participant,in this case i-th slave 118, and accordingly 2 is added to a remainderof a division.

Usually, during synchronization of the m-sequences of block-synchronizedscramblers 110 in a sending and a receiving participant in the case of acontinuous bit stream, sequence errors may occur over all the messages.To remedy this, synchronization by the inter-frame symbol is used withinthe scope of the exemplary embodiments and/or exemplary methods of thepresent invention. In one configuration of block-synchronized scrambler110 it is provided that the bit stream of the data packets does notcorrespond to the m sequence. It is furthermore possible to allow for nointer-frame symbols to be generated at the output of themodulo-2-addition of the bit stream with the m-sequence. Using thatencoding method, it is also possible to encode the frames, usually emptyframes, to individual participants while other participants, possiblyinexpensive participants or participants having small frame lengths,include no encoding for spectral spreading. A combination of diverseencoding methods is also possible.

Using the method, in an embodiment of the invention transmission of databetween participants of a serial, ring-shaped communications arrangement2 is possible. In that communications arrangement 2, the participantsare serially connected to one another, a data packet 30, 50, 56, 62, 74being passed from a participant provided as master 4 to furtherparticipants provided as slaves 6, 8, 10, data packet 30, 50, 56, 62, 74being passed from slave 6, 8, 10 to slave 6, 8, 10. Contents of datapacket 30, 50, 56, 62, 74 include address information. That addressinformation may be arranged in an address field 40, 43 of data packet30, 50, 56, 62, 74 and may be in the form of an address value. Inembodiment of the method, the address value and hence the addressinformation of received data packet 30, 50, 56, 62, 74 is altered, forexample, by a fixed value by each slave 6, 8, 10.

It is provided in this case that the address field 40, 43 may be in anydesired position within a data packet 30, 50, 56, 62, 74. Accordingly,modification of a data packet 30, 50, 56, 62, 74 is carried out by aslave 6, 8, 10. Each slave 6, 8, 10 alters an address value and hencethe address information within a data packet 30, 50, 56, 62, 74 in thesame manner, the same mathematical operation, usually addition orsubtraction, being carried out by each slave 6, 8, 10. In addition, inan exemplary embodiment of the present invention, all slaves 6, 8, 10have the same, identical address.

What is claimed is:
 1. A method for transmitting data betweenparticipants of a serial, ring-shaped communications arrangement, inwhich the participants are serially connected to one another, the methodcomprising: passing a data packet from a participant provided as amaster to further participants provided as slaves, wherein the datapacket is passed from one of the slaves to another of the slaves; andprioritizing an interrupt received at the master from the slaves on thebasis of the position of the slave having sent the interrupt in thering-shaped communications arrangement; wherein a protocol for prioritycontrol is provided with which at least one slave transmits a request tothe master via a data packet including an empty frame.
 2. The method ofclaim 1 wherein the slaves have identical local addresses, and whereinan identical algorithm for communication is stored in each of theslaves.
 3. The method of claim 1, wherein encoding for recovery oftiming information from a signal is used for a data packet that is to betransmitted, wherein a parity bit is inserted equidistantly in the dataframe by that encoding, so that a bit stream for transmission of datapackets has at least one edge change within a specified period of time.4. The method of claim 1, wherein the data are transmitted continuously,and wherein the data packet includes with an address field useful dataprovided for a slave.
 5. The method of claim 1, wherein, as addressinformation, an address value of the received data packet is altered byone of adding and subtracting a fixed value by each slave.
 6. Acommunications arrangement, which has a ring-shaped configuration,comprising: a plurality of participants which are serially connected toone another, wherein one of the participants is a master and other onesof the participants are slaves; wherein the master is configured to passthe data packet to the slaves, each of the slaves passing the datapacket to a subsequent one of the slaves; wherein interrupts received atthe master from the slaves are prioritized on the basis of the positionof the slave having sent the interrupt in the ring-shaped communicationsarrangement; and wherein a protocol for priority control is providedwith which at least one slave transmits a request to the master via adata packet including an empty frame.
 7. The communications arrangementof claim 6, wherein each participant has at least one serial interfacewith which the participant is connected via a communications connectionhaving a serial interface to an adjacent participant of thecommunications arrangement.